JP2002359569A - Broadcasting receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a demodulation signal with less quantization noise and improved C/N ratio, even though an A/D converter and a digital demodulator are shaped by a double modulation type signal processing when receiving broadcasting where FM broadcasting and multi-carrier transmission type digital broadcasting are being performed simultaneously at nearly the same center frequency. SOLUTION: The broadcasting receiver comprises an IF amplification section 11 for amplifying IF signals, a band elimination filter(BEF) 12 for attenuating a frequency near the center frequency of the IF signal, an A/D converter 27 for converting an analog signal that has passed through the BEF 12 to a digital signal, and a digital demodulator 29 for digitally demodulating the signal of analog broadcasting or that of digital broadcasting outputted by the A/D converter 27. The BEF 12 attenuates only the signal component of analog broadcasting mainly, and sets the amplitude of the signal of analog broadcasting and that of the signal of digital broadcasting nearly the same, before outputting it to the ADC 27.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus compatible with a broadcasting system in which analog broadcasting and digital broadcasting are simultaneously broadcast at substantially the same center frequency, and more particularly, to a broadcasting system using the two modulation systems with a common tuner. The present invention relates to a broadcast receiving device for receiving.

[0002]

2. Description of the Related Art Recently, a broadcasting system has been proposed in which analog broadcasting and digital broadcasting are simultaneously broadcast from the same broadcasting location. For example, the IB proposed by the US FCC
A broadcast system called an OC (In Band On Channel) system corresponds to this. The modulation method in the IBOC system is also called an FM-iDAB method. The IBOC
In the digital broadcasting in the system, a multi-carrier transmission system is used. In a digital broadcasting using such a multi-carrier transmission system and an analog broadcasting / digital broadcasting / broadcasting receiving device capable of receiving an analog broadcasting, the channel is tuned (tuned). In the case where analog broadcast signals and digital broadcast signals are mixed near the frequency, the amplitude of the signal related to analog broadcasting is much larger than the amplitude of the signal related to digital broadcasting. There are various problems.

For example, in the IBOC system, FM audio broadcasts, which are analog broadcasts, are arranged at intervals of 400 kHz, and broadcasting is performed such that the spectrum of the digital broadcast exists in the gap between the spectrums of the FM audio broadcast. Are substantially the same. Digital broadcasting is, for example, a European standard (Eureka 14).
This is a broadcast similar to digital audio broadcast by a DAB system (standard is ETS300401) conforming to 7). The DAB signal in the DAB system is an orthogonal frequency division multiplex modulation scheme, that is, an OFDM (Orthogonal Frequency).
The signal is transmitted as an OFDM signal that has been modulated by Entity Division Multiplex.

[0004] When receiving near a certain frequency in which an OFDM modulated signal of digital audio broadcasting and an FM modulated signal of analog broadcasting are mixed, an intermediate frequency signal (IF signal) generated from the received RF signal is used. In a predetermined frequency range, an FM audio broadcast signal having a large amplitude and a digital broadcast signal composed of a large number of carriers having a small amplitude are mixed.

Hereinafter, a first example of a conventional analog / digital combined broadcast receiving apparatus will be described with reference to FIG.
FIG. 7 is a block diagram showing a first example of a conventional analog / digital broadcast receiver. In the following description, a case where analog broadcasting is FM broadcasting will be described as an example. In the analog / digital radio broadcast receiving apparatus 30 shown in FIG. 7, a desired frequency is selected by the RF amplifying section 52 from the signal supplied from the antenna 51, and the mixer (MI) is selected.
XER) 53. The mixer 53 generates an intermediate frequency signal (IF signal) to generate a band pass filter (BPF) 5.
4 and a band elimination filter (BEF) 57. The BPF 54 supplies only a signal relating to analog broadcasting distributed near the center frequency of the IF signal to the IF amplifier circuit 55. The BEF 57 removes a signal related to analog broadcasting distributed near the center frequency from the IF signal,
Only a signal related to digital broadcasting is given to the IF amplifier circuit 58.

The analog broadcast signal output from the IF amplifier circuit 55 is demodulated by an FM demodulator 56, amplified by an audio amplifier 62, and its sound is output from a speaker 63. On the other hand, the digital broadcast signal output from the IF amplifying circuit 58 is converted into a digital signal by an A / D converter (ADC) 59, digitally demodulated by a digital demodulator 60, and a D / A converter (DAC) 61 Is converted to an analog signal, amplified by the audio amplifier 62, and the sound is output from the speaker 63. The audio amplifier 62 normally selects and outputs one of an analog broadcast and a digital broadcast. The amplitude of the output of the IF amplification circuit 55 is set to an optimum level for FM demodulation by the FM demodulator 56, and the amplitude of the output of the IF amplification circuit 58 is the ADC 59
Is set so that the largest resolution can be obtained when A / D conversion is performed. The RF amplifier 52, the IF amplifier 55, and the IF amplifier 58 are subjected to automatic gain control (hereinafter, also referred to as AGC) for automatically controlling their gains, but the description thereof is omitted here. .

Next, a second example of a conventional analog / digital broadcast receiver will be described with reference to FIG.
FIG. 8 is a block diagram showing a second example of a conventional analog / digital broadcast receiving apparatus. In the analog / digital combined radio broadcast receiving apparatus 40 shown in FIG.
A desired frequency is tuned by the RF amplifier 52 from the signal supplied from the antenna 51, and is given to the filter 71. The filter 71 is a bandpass filter (BPF) for removing unnecessary frequency components, and its output is a mixer (MIX).
ER) 72. The mixer 72 generates an IF signal and supplies the IF signal to the IF amplifier circuit 73. IF amplification circuit 73
An analog broadcast signal and a digital broadcast signal included in the F signal are both amplified and given to an A / D converter (ADC) 74.

The ADC 74 converts an analog broadcast signal and a digital broadcast signal into a digital signal, and supplies the digital signal to a digital demodulator 75 that performs digital demodulation. In the digital demodulator 75, an analog broadcast signal or a digital broadcast signal is digitally demodulated by a demodulation method corresponding to a modulation method, and decoding of a compressed signal is performed as necessary.
Digital data is output from the digital demodulator 75 and a demodulated audio signal is output to the DAC 77. The DAC 77 converts a digital signal obtained by demodulation and / or decoding into an analog signal. DAC
The output of 77 is amplified by the audio amplifier 62, and the sound is output from the speaker 63. The RF-AGC voltage generation circuit 77 generates an AGC voltage from the IF signal output from the MIXER 72 and supplies the AGC voltage to the RF amplifier 52. I
The F-AGC voltage generation circuit 76 generates an AGC control signal based on the I signal or the Q signal of the baseband signal obtained by the quadrature demodulation in the digital demodulator 75 and supplies the same to the IF amplification circuit 73. The digital demodulator 75 outputs digital data in addition to the audio data supplied to the DAC 77.

In the first prior art apparatus shown in FIG. 7, when a signal is received at a certain frequency, an analog broadcast signal and a digital broadcast signal are mixed in the vicinity of the received frequency. However, demodulation of an analog broadcast signal and digital broadcast signal are demodulated by separate demodulators. The level (amplitude) of the signal applied to each demodulator and the ADC 59 is determined by the IF amplifier 55 and the IF amplifier 58.
By adjusting the degree of amplification, an appropriate value can be set. Therefore, the quantization error generated in the ADC 59 can be reduced. However, since separate demodulators are used for analog broadcasting and digital broadcasting, the circuit becomes complicated and the manufacturing cost is high.

On the other hand, in the second prior art apparatus shown in FIG.
Since the demodulation of the analog broadcast signal and the digital broadcast signal are demodulated by one common demodulator, there is no problem as in the first conventional apparatus. However, the signal is input to the ADC 74 in a state where the amplitude of the analog broadcast signal is much larger than the amplitude of the digital broadcast signal, and the ADC 74 performs A / D conversion on the analog broadcast signal and the digital broadcast signal together. For this reason, when the level of the analog broadcast signal is set to be suitable for the ADC 74, the number of effective bits of the ADC 74 decreases in the digital broadcast signal, and the quantization error in the ADC 74 increases in the broadcast of a low signal level. There is a problem that the C / N and distortion of the demodulated signal generated by the demodulator 75 increase.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to simultaneously perform analog broadcasting and digital broadcasting by a multicarrier transmission system at substantially the same center frequency. When receiving an existing broadcast, a demodulated signal with a small quantization noise and a large C / N ratio can be obtained despite the fact that the A / D converter and the digital demodulator are shared for both modulation signal processing. It is to provide a broadcast receiving device.

[0012]

Means for Solving the Problems The present invention has the following structure to achieve the above object. First
According to the invention, in a broadcast receiving apparatus for receiving a broadcast in which analog and digital broadcasts having substantially the same center frequency of a carrier wave are mixed, an IF amplifying unit for amplifying an intermediate frequency signal; A filter for attenuating, an A / D converter for converting an analog signal passing through the filter into a digital signal, and a digital demodulation for digitally demodulating an analog broadcast signal and / or a digital broadcast signal output from the A / D converter And a filter, wherein the filter attenuates the amplitude of the analog broadcast signal, and outputs the analog broadcast signal with substantially the same amplitude as the digital broadcast signal.

According to a second aspect, in the broadcast receiving apparatus according to the first aspect, the filter is a band elimination filter or a trap filter capable of controlling the maximum attenuation.

According to a third aspect, in the broadcast receiving apparatus according to the second aspect, the filter has a resonance circuit, and a maximum attenuation of the filter is changed by changing a Q value (Quality factor) of the resonance circuit. This is a broadcast receiving device that controls the broadcast reception.

According to a fourth aspect, in the broadcast receiving apparatus according to the third aspect, the comparator for comparing the amplitude of the digital broadcast signal in the intermediate frequency signal input to the filter with the amplitude of the output signal of the filter. This is a broadcast receiving device provided with:

According to a fifth aspect of the present invention, in the broadcast receiving apparatus according to the third aspect of the present invention, the value of the Q is controlled by changing an internal resistance of a semiconductor active element connected in series to the series resonance circuit. Device.

A sixth aspect of the present invention is the broadcast receiving apparatus according to the fourth or fifth aspect, wherein the value of the Q is controlled in accordance with the output of the comparator.

According to a seventh aspect, in the broadcast receiving apparatus according to any one of the first to fourth aspects, the signal for automatic gain control of the RF amplifier or the IF amplifier is generated from the output of the filter. This is a broadcast receiving apparatus.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A broadcast receiving apparatus according to the present invention is a broadcast receiving apparatus for receiving a broadcast in which an analog broadcast and a digital broadcast having substantially the same center frequency of a carrier wave are mixed, and an intermediate output from a mixer. An IF amplifier for amplifying a frequency signal, a filter for attenuating a frequency near the center frequency of the intermediate frequency signal, an A / D converter for converting an analog signal passing through the filter into a digital signal,
A digital demodulator for digitally demodulating an analog broadcast signal and / or a digital broadcast signal output by the converter, wherein the analog broadcast signal and the digital broadcast signal input to the A / D converter have substantially the same amplitude. A broadcast receiving apparatus wherein the amplitude of an analog broadcast signal is attenuated by the filter.

Hereinafter, embodiments of the present invention will be described. First, as an example where analog broadcasting and digital broadcasting are broadcast simultaneously from the same antenna,
The IBOC system proposed by the Federal Communications Committee (USA) will be described with reference to FIG. FIG. 3 is a diagram showing a power spectrum distribution at the time of transmission in the IBOC system broadcasting system. In FIG. 3, the horizontal axis represents frequency, and the center frequency of FM audio broadcast, which is analog broadcasting, is set to 0, and the deviation from the center frequency is shown. The vertical axis indicates the intensity of the power spectrum in the broadcast wave, the dotted line is for FM audio broadcasting, and the solid line is for digital audio broadcasting that is broadcast using gaps in FM audio broadcasting. The center frequency of the digital audio broadcast is the same as that of the analog broadcast.

The FM audio broadcasts are arranged at intervals of 400 kHz. That is, adjacent FM audio broadcasts are arranged such that their center frequencies are separated by 400 kHz. The center frequency of digital audio broadcasting is F
It is the same as the center frequency of the M audio broadcast, and the power spectrum of the digital audio broadcast wave is distributed outside the power spectrum of the FM audio broadcast wave. For example, the power spectrum intensity of the FM audio broadcast wave indicated by a dotted line has a slope of about 0.35 dB / kHz, and the power spectrum is distributed within a range of approximately ± 129 kHz with respect to the center frequency.

On the other hand, the power spectrum of the digital audio broadcast wave shown by the solid line is ± (129
(kHz to 199 kHz). When analog broadcasting and digital broadcasting are performed at the same time as in the IBOC system broadcasting system, they are transmitted from the same antenna and received by the same antenna. Therefore, the power spectrum intensity as shown in FIG. 3 is broadcast at a predetermined ratio between analog broadcasting and digital broadcasting, and has the same ratio at the time of reception. For example, in the example of FIG. 3, the analog broadcast is -17 dB, and the digital broadcast is -4 dB.
At 2 dB, the difference is 25 dB.

In the IBOC system, even if an FM audio broadcast and a digital audio broadcast are simultaneously broadcast at the same center frequency, the two power spectra are prevented from overlapping each other to prevent mutual interference and to enable simultaneous broadcast. Is what you do. In addition to the case where analog broadcasting and digital broadcasting are performed at the same time as in the above-mentioned IBOC system, the radio wave environment may include only analog broadcasting or digital broadcasting only.

FIG. 1 is a block diagram showing a first embodiment of the broadcast receiving apparatus according to the present invention. In the following description, analog broadcasting is FM audio broadcasting, and digital broadcasting is DAB.
The case of audio broadcasting will be described as an example. Also,
In this DAB system, OFDM (Orthogonal Frequency Division Multiplexing: Orthogonal Frequency Division) is used as a modulation method.
Multiplex) will be described. In the broadcast receiving apparatus 10 shown in FIG. 1, the antenna 5 shown in FIG.
1, an RF amplifier 52 and a mixer 53 are used to generate an AGC control signal based on the amplitude of the IF signal,
Are subjected to AGC, but their illustration is omitted.
In FIG. 1, an IF signal (intermediate frequency signal) output from a mixer 53 is amplified by an IF amplifier 11, and a band elimination filter (BEF) 12 and an A / D converter (A).
DC) 27 to a digital demodulator 29.

The AGC voltage generator 35 is a band eliminator.
The AGC voltage is generated by detecting the amplitude of the output signal of the filter (BEF) 12 and supplied to the IF amplifier 11. As a result, the amplitude of the IF signal input to the ADC 27 is maintained at a substantially constant value. In the BEF 12, the digital broadcast signal in the input signal is passed almost as it is, only the FM broadcast signal is attenuated by a predetermined amount, and the amplitude of the digital broadcast signal and the FM broadcast signal is made substantially equal. / D
The signal is given to a converter (ADC) 27. The ADC 27 converts an analog signal into a digital signal and supplies the digital signal to a digital demodulator 29 which performs digital demodulation.

The digital demodulator 29 includes a quadrature demodulator for generating an I signal and a Q signal of a baseband signal. The digital demodulator 29 performs an arithmetic operation on the I signal and the Q signal by an arithmetic method according to a modulation method, and performs digital broadcasting. Demodulate the signal and / or the analog broadcast signal. The digital demodulator 29 includes a channel decoder and an MPEG decoder. The channel decoder performs de-interleaving for returning the order of signals to the original order, and detection and correction of error codes. Digital data and an audio signal are output from the digital demodulator 29. The audio signal is converted to an analog signal by the DAC 31, amplified by the audio amplifier 33, and the sound is output from the speaker.

FIG. 4 shows a BEF 12 and a filter 2 described later.
2 shows a specific circuit example of the BEF 12. As shown in FIG. 4, the center frequency f0 of the IF signal
The analog broadcast signal components distributed in the vicinity have a gain of g0.
To g1, and the digital broadcast signal distributed outside the frequency at which the analog broadcast signal is distributed is not attenuated, indicating that the gain is g0. In the example described with reference to FIG. 3, the difference between g0 and g1 is 25 dB. FIG. 2 shows a BEF including three LC resonance circuits. The Q value (Quality factor) of the resonance circuit is fixed to a predetermined value, and the attenuation at the center frequency f0 of the IF signal is set to a predetermined value. The value of Q of the resonance circuit is set to a predetermined value by the resistor 46.

FIG. 5 is a block diagram showing a second embodiment of the broadcast receiving apparatus according to the present invention. In the apparatus of the first embodiment shown in FIG. 1 and the apparatus of the second embodiment shown in FIG. 5, the same elements are denoted by the same reference numerals, and the description thereof will be omitted. The main difference between the apparatus of the second embodiment of FIG. 5 and the apparatus of the first embodiment of FIG.
2 instead of band elimination filter (BEF) 1
3. The point is that a peak detector 15, a comparator 17, a Q control signal generator 19, a filter 21, and a peak detector 25 are provided.

The BEF 13 removes analog broadcast signals distributed near the center frequency of the IF signals output from the IF amplifying unit 11, and supplies only digital broadcast signals to the peak detector 15, and the peak detector 15 The peak value of the digital broadcast signal is detected and given to the comparator 17. The filter 21 is composed of a trap circuit capable of controlling the amount of attenuation or a BEF capable of controlling the amount of attenuation. The filter 21 allows the digital broadcast signal in the input signal to pass substantially as it is, The broadcast signal is attenuated by a predetermined amount so that the amplitudes of the digital broadcast signal and the FM broadcast signal are substantially equal, and then the A / D converter (AD)
C) Give to 27.

The output of the filter 21 is provided to a peak detector 25. The peak detector 25 detects the peak value of the applied signal and supplies the detected signal to the comparator 17. The comparator 17 compares a value obtained by subtracting a predetermined value from the output of the peak detector 15 with the output of the peak detector 25, and gives the comparison result to the Q control signal generation unit 19. The Q control signal generator 19 controls the Q value of the filter 21 according to the output of the comparator 17.
A control signal is generated and given to the filter 21. Filter 2
In 1, the value of Q of the resonance circuit is changed according to the Q control signal given from the Q control signal generator 19, and the attenuation of the analog broadcast signal is controlled. Thereby, the peak detector 2
5 is controlled to be larger than the output of the peak detector 15 by a predetermined value, and the amplitudes of the analog broadcast signal and the digital broadcast signal supplied to the ADC 27 are controlled to be substantially equal. In addition, a BPF that allows only an analog broadcast signal to pass is provided between the filter 21 and the peak detector 25,
The comparator 17 may compare the peak value of the digital broadcast signal output from the peak detector 15 with the peak value of the analog broadcast signal output from the peak detector 25.

FIG. 6 shows a specific circuit example of the filter 21, and its attenuation characteristics are shown in FIG. The difference between the filter circuit shown in FIG. 6 and the filter circuit shown in FIG. 2 is that an FET 48 is provided instead of the resistor 46 in FIG. The internal resistance between the source and the drain of the FET 48 is connected in series to a series resonance circuit formed by the inductance 44 and the capacitor 45, and the internal resistance between the source and the drain is controlled by a Q control signal applied to the gate of the FET 48. Then, the value of Q of the resonance circuit is controlled. Note that F
Of course, the ET 48 may be another semiconductor active element capable of controlling the resistance between terminals.

As shown in FIG. 4, the amount of attenuation of the analog broadcast signal by the filter 21 is small when Q is small, and large when Q is large. FIG.
As shown in (2), the analog broadcast signal near the center frequency f0 of the IF signal is controlled by the control loop so that the gain becomes g1. In the example described with reference to FIG.
And g1 is 25 dB.

As described above in detail, according to the broadcast receiving apparatus of the present invention, when receiving a mixed broadcast of analog broadcast and digital broadcast, the analog broadcast signal and the digital broadcast signal are shared. The signal is processed by the / D converter and then demodulated by the shared digital demodulator. A / D
Since the amplitude of the analog broadcast signal input to the converter and the amplitude of the digital broadcast signal are made equal by the control loop, the quantization error caused by the A / D converter for both the analog broadcast signal and the digital broadcast signal. Can be set to minimize the A / D converter, the distortion of the demodulated signal can be reduced, and the C / N ratio can be improved.

Further, according to the present invention, the amount of attenuation of the signal of the analog broadcast component can be easily controlled by changing the value of Q of the resonance circuit. Then, the internal resistance (resistance between terminals) of the FET, the transistor, and the like can be easily controlled according to the output of the comparator.

Further, according to the present invention, the signal (the output of the BEF 12 or the filter) input to the A / D converter is output.
An AGC voltage applied to the RF amplification unit or the IF amplification unit can be generated based on the output of r21). At the input terminal of the shared A / D converter, the analog broadcast signal and the digital broadcast signal have the same amplitude,
This has the effect of eliminating the need to switch AGC depending on whether the received broadcast is an analog broadcast or a digital broadcast. Compared with the conventional method shown in FIG. 2 in which the levels of the demodulated I and Q signals are detected to obtain an AGC control signal, the AGC according to the present invention has no delay time required for digital demodulation, and AGC promptly in the department
Operation is started.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a broadcast receiving apparatus according to the present invention.

FIG. 2 is a diagram showing a specific example of a BEF 12 used in the present invention.

FIG. 3 is a diagram showing a power spectrum distribution at the time of transmission in the IBOC system broadcasting system.

FIG. 4 is a diagram showing attenuation characteristics of a BEF 12 and a filter 21 used in the present invention.

FIG. 5 is a block diagram showing a second embodiment of the broadcast receiving apparatus according to the present invention.

FIG. 6 is a diagram showing a specific example of a filter 21 used in the present invention.

FIG. 7 is a block diagram showing a first example of a conventional analog / digital combined broadcast receiving apparatus.

FIG. 8 is a block diagram showing a second example of a conventional analog / digital combined broadcast receiving apparatus.

[Explanation of symbols]

 Reference Signs List 11 IF amplifying unit 12, 13 Band elimination filter (BEF) 15, 25 Peak detector 17 Comparator 19 Q control signal generator 21 Filter 27 A / D converter (ADC) 29 Digital demodulator 31 D / A converter (DAC) 48 FET

Claims (7)

[Claims] 1. A broadcast receiving apparatus for receiving a broadcast in which analog and digital broadcasts having substantially the same center frequency of a carrier wave are mixed, comprising: an IF amplifier for amplifying an intermediate frequency signal; , An A / D converter for converting an analog signal passing through the filter into a digital signal, and a digital for digitally demodulating an analog broadcast signal and / or a digital broadcast signal output from the A / D converter. A demodulator, wherein the filter attenuates the amplitude of the analog broadcast signal,
A broadcast receiving apparatus for outputting an analog broadcast signal having an amplitude substantially equal to that of a digital broadcast signal. 2. The broadcast receiving apparatus according to claim 1, wherein said filter is a band elimination filter or a trap filter capable of controlling the maximum attenuation. 3. The broadcast according to claim 2, wherein the filter has a resonance circuit, and the maximum attenuation of the filter is controlled by changing a Q value (Quality factor) of the resonance circuit. Receiver. 4. The broadcast receiving apparatus according to claim 3, further comprising a comparator for comparing the amplitude of the digital broadcast signal in the intermediate frequency signal input to the filter with the amplitude of the output signal of the filter. apparatus. 5. The broadcast receiving apparatus according to claim 3, wherein the value of Q is controlled by changing an internal resistance of a semiconductor active element connected in series to the series resonance circuit. 6. The broadcast receiving apparatus according to claim 4, wherein the value of said Q is controlled according to an output of said comparator. 7. The broadcast receiving apparatus according to claim 1, wherein a signal for automatic gain control of an RF amplifier or said IF amplifier is generated from an output of said filter.